Showing papers on "Antigen published in 1988"
TL;DR: A human IgGI antibody has been reshaped for serotherapy in humans by introducing the six hypervariable regions from the heavy- and light-chain variable domains of a rat antibody directed against human lymphocytes.
Abstract: A human IgGI antibody has been reshaped for serotherapy in humans by introducing the six hypervariable regions from the heavy- and light-chain variable domains of a rat antibody directed against human lymphocytes. The reshaped human antibody is as effective as the rat antibody in complement and is more effective in cell-mediated lysis of human lymphocytes.
3,167 citations
TL;DR: This view of T-cell recognition has implications for how the receptors might be selected in the thymus and how they (and immunoglobulins) may have arisen during evolution.
Abstract: The four distinct T-cell antigen receptor polypeptides (alpha, beta, gamma, delta) form two different heterodimers (alpha:beta and gamma:delta) that are very similar to immunoglobulins in primary sequence, gene organization and modes of rearrangement. Whereas antibodies have both soluble and membrane forms that can bind to antigens alone, T-cell receptors exist only on cell surfaces and recognize antigen fragments only when they are embedded in major histocompatibility complex (MHC) molecules. Patterns of diversity in T-cell receptor genes together with structural features of immunoglobulin and MHC molecules suggest a model for how this recognition might occur. This view of T-cell recognition has implications for how the receptors might be selected in the thymus and how they (and immunoglobulins) may have arisen during evolution.
2,858 citations
TL;DR: The mechanism of self-tolerance is studied in T-cell-receptor transgenic mice expressing a receptor in many of their T cells for the male (H–Y) antigen in the context of class I H–2Db MHC antigens.
Abstract: The mechanism of self-tolerance is studied in T-cell-receptor transgenic mice expressing a receptor in many of their T cells for the male (H-Y) antigen in the context of class I H-2Db MHC antigens. Autospecific T cells are deleted in male mice. The deletion affects only transgene-expressing cells with a relatively high surface-density of CD8 molecules, including nonmature CD4+ CD8+ thymocytes, and is not caused by anti-idiotype cells.
1,673 citations
TL;DR: Results are consistent with a model for transformation by SV40 which, at least in part, involves T/p110-114 complex formation and the perturbation of Rb protein and/or T function.
1,466 citations
TL;DR: Findings indicate that self tolerance may result from mechanisms other than clonal deletion, and are consistent with the hypothesis that IgD may have a unique role in B-cell tolerance.
Abstract: Immunological tolerance has been demonstrated in double-transgenic mice expressing the genes for a neo-self antigen, hen egg lysozyme, and a high affinity anti-lysozyme antibody. The majority of anti-lysozyme B-cells did not undergo clonal deletion, but were no longer able to secrete anti-lysozyme antibody and displayed markedly reduced levels of surface IgM while continuing to express high levels of surface IgD. These findings indicate that self tolerance may result from mechanisms other than clonal deletion, and are consistent with the hypothesis that IgD may have a unique role in B-cell tolerance.
1,441 citations
TL;DR: Rat bone marrow chimeras and encephalitogenic, major histocompatability--restricted T-helper lymphocytes were used to show that a subset of endogenous CNS cells, commonly termed "perivascular microglial cells," is bone marrow-derived and are fully competent to present antigen to lymphocytes in an appropriately restricted manner.
Abstract: A crucial question in the study of immunological reactions in the central nervous system (CNS) concerns the identity of the parenchymal cells that function as the antigen-presenting cells in that organ. Rat bone marrow chimeras and encephalitogenic, major histocompatability--restricted T-helper lymphocytes were used to show that a subset of endogenous CNS cells, commonly termed "perivascular microglial cells," is bone marrow-derived. In addition, these perivascular cells are fully competent to present antigen to lymphocytes in an appropriately restricted manner. These findings are important for bone marrow transplantation and for neuroimmunological diseases such as multiple sclerosis.
1,410 citations
TL;DR: It is shown that a large binding site for a protein antigen (lysozyme) can also be transplanted from mouse to human heavy chain and facilitated by an induced-fit mechanism.
Abstract: The production of therapeutic human monoclonal antibodies by hybridoma technology has proved difficult, and this has prompted the "humanizing" of mouse monoclonal antibodies by recombinant DNA techniques. It was shown previously that the binding site for a small hapten could be grafted from the heavy-chain variable domain of a mouse antibody to that of a human myeloma protein by transplanting the hypervariable loops. It is now shown that a large binding site for a protein antigen (lysozyme) can also be transplanted from mouse to human heavy chain. The success of such constructions may be facilitated by an induced-fit mechanism.
1,390 citations
TL;DR: The results suggest that xenogeneic transplantation of human lymphoid cells into SCID mice may provide a useful model for the study of normal human immune function, the response of the immune system to pathogenic agents and early events in lym-phomagenesis.
Abstract: The pressing need for a better experimental system for AIDS research has brought into sharp focus the shortcomings of available animal models and the practical and ethical limitations of studies of immune responses and viral pathogenesis in humans. Current studies of the human immune responses are limited to relatively restrictive in vivo experiments and several in vitro systems that, although useful, allow only short-term studies and support responses to a few antigens. Neither model is particularly amenable to studies of the pathogenesis of diseases of the immune system. We report here that injection of human peripheral blood leukocytes (PBL) can result in the stable long-term reconstitution of a functional human immune system in mice with severe combined immunodeficiency (SCID). Human PBL transplanted to SCID mice increase in number and survive for at least six months; reconstituted mice show spontaneous secretion of human immunoglobulin and a specific human antibody response is induced following immunization with tetanus toxoid. All of the major cell populations present in PBL are found in the lymphoid tissue and blood of SCID recipients, although the relative proportions of B cells, T-cell subsets and monocytes/macrophages in long-term recipients differ from those found in normal PBL and, in mice transplanted with 50 x 10(6) or more PBL from Epstein-Barr virus (EBV)-seropositive donors, EBV-positive B-cell lymphomas often develop. Our results suggest that xenogeneic transplantation of human lymphoid cells into SCID mice may provide a useful model for the study of normal human immune function, the response of the immune system to pathogenic agents and early events in lymphomagensis.
1,257 citations
Patent•
07 Jan 1988
Abstract: A chimeric antibody with human constant region and murine variable region, having specificity to a 35 kDA polypeptide (Bp35(CD20)) expressed on the surface of human B cells, methods of production, and uses.
1,231 citations
TL;DR: The hypothetical class II foreign-antigen binding site presented is consistent with mutation experiments1828 and provides a structural framework for proposing peptide binding models to help understand recent peptidebinding data11,2933.
Abstract: Class II and class I histocompatibility molecules allow T cells to recognize 'processed' polypeptide antigens1–5. The two polypeptide chains of class II molecules, α and β, are each composed of two domains (for review see ref. 6); the N-terminal domains of each, α1 and β1, are highly polymorphic6–10 and appear responsible for binding peptides at what appears to be a single site11–13 and for being recognized by MHC-restricted antigen-specific T cells14,15. Recently, the three-dimensional structure of the foreign antigen binding site of a class I histocompatibility antigen has been described16,17. Because a crystal structure of a class II molecule is not available, we have sought evidence in class II molecules for the structural features observed in the class I binding site by comparing the patterns of conserved and polymorphic residues of twenty-six class I and fifty-four class II amino acid sequences. The hypothetical class II foreign-antigen binding site we present is consistent with mutation experiments18–28 and provides a structural framework for proposing peptide binding models to help understand recent peptide binding data11,29–33.
1,077 citations
TL;DR: The presence of Mlsa/ MHC during T-cell development results in the deletion of T cells that express Vβ8.1, documenting the importance of clonal deletion in establishing tolerance to self antigens.
Abstract: In mice the product of the Mlsa locus is an unusual antigen capable of interaction with certain products of the major histocompatibility locus (MHC) to form a ligand for a large portion of the T-cell alpha/beta receptor repertoire, including nearly all receptors that use V beta 8.1. The presence of Mlsa/MHC during T-cell development results in the deletion of T cells that express V beta 8.1, documenting the importance of clonal deletion in establishing tolerance to self antigens.
Journal Article•
TL;DR: The recovery of virtually all all alloantigen induced secondary proliferative response in the UCHL 1+,CD45R- T cell population suggests that UCHL1 identifies a primed population of T cells which may include memory cells.
Abstract: A group of mAb recognizing the 200- and/or 220-kDa determinants (CD45R) of the leukocyte common Ag such as 2H4, WR16, MD4.3, and SN130 cross-block each other showing that they recognize a closely related epitope. The antibody UCHL1 reacts with a 180-kDa determinant of the leukocyte common Ag and exhibits a reciprocal T subset distribution pattern to the CD45R group. Peripheral blood T cells were 40% positive for UCHL1 and 58 to 65% positive for the CD45R antibodies; less than 1% of cells stained for both. On activation of CD45R+,UCHL1- T cells by PHA, up to 40% of cells became positive for both CD45R and UCHL1 by day 3. By day 7, CD45R+,UCHL1- cells fell from 90 to less than 21% whereas UCHL1+,CD45R- cells rose from 2 to 93%. Conversely, PHA-stimulated UCHL1+,CD45R- cells remained UCHL1+,CD45R- during the 7 days in culture showing that phenotypic change was unidirectional from CD45R+ to UCHL1+. In primary allogeneic mixed lymphocyte reactions, activated CD45R+ T cells also showed a change to UCHL1+. When these cells were rechallenged by the original alloantigen, the UCHL1+ cells showed 7- to 20-fold greater proliferation than the CD45R+ cells on day 3 after rechallenge. The recovery of virtually all alloantigen induced secondary proliferative response in the UCHL1+,CD45R- T cell population suggests that UCHL1 identifies a primed population of T cells which may include memory cells.
TL;DR: T lymphocytes reactive with the product of the Mlsa-allele of the minor lymphocyte stimulating (Mls) locus use a predominant T-cell receptor β-chain variable gene segment (Vβ6), consistent with a model in which tolerance to self antigens is achieved by clonal deletion.
Abstract: T lymphocytes reactive with the product of the Mlsa-allele of the minor lymphocyte stimulating (Mls) locus use a predominant T-cell receptor beta-chain variable gene segment (V beta 6). Such V beta 6-bearing T cells are selectively eliminated in the thymus of Mlsa-bearing mice, consistent with a model in which tolerance to self antigens is achieved by clonal deletion.
TL;DR: To characterize the critical M. tuberculosis epitope, AA T-cell clones were used to screen mycobacterial antigens expressed in Escherichia coli and genetically engineered truncated proteins and synthetic peptides and recognized an epitope formed by the amino acids at positions 180–188 in the sequence of a Mycobacterium bovis BCG antigen.
Abstract: Adjuvant arthritis (AA) is a chronic disease inducible in rats by immunization with an antigen of Mycobacterium tuberculosis1. After the isolation of arthritogenic T-cell lines2 and clones3, it became possible to demonstrate that the critical M. tuberculosis antigen contained an epitope cross-reactive with a self-antigen in joint cartilage4–6. Like AA rats, patients suffering from rheumatoid arthritis demonstrated specific T-lymphocyte reactivity to the M. tuberculosis fraction containing the cross-reactive epitope7. To characterize the critical M. tuberculosis epitope we used AA T-cell clones to screen mycobacterial antigens expressed in Escherichia coli and genetically engineered truncated proteins and synthetic peptides. The AA T-cell clones recognized an epitope formed by the amino acids at positions 180–188 in the sequence of a Mycobacterium bovis BCG antigen8. Administration of this antigen to rats induced resistance to subsequent attempts to produce AA.
Journal Article•
TL;DR: Data implicate IFN-gamma as a suppressive factor for the proliferation of the subset of HTL designated Th2, and suggest that the relative amounts of the various lymphokines present during an immune response may direct which T cell types increase in number.
Abstract: A biphasic dose-response curve was observed when the IL-1-dependent HTL clone D10 was exposed to IL-1 plus supernatants from some activated T cell clones but not others. The active component that inhibited proliferation at high concentrations of these supernatants appeared to be IFN-gamma based on the following findings: 1) the biphasic pattern of responsiveness correlated with the presence of IFN-gamma in the supernatants; 2) an anti-IFN-gamma mAb augmented the proliferation of D10 cells to these supernatants; 3) rIFN-gamma inhibited profoundly the response of D10 cells stimulated with rIL-1 plus supernatant from activated D10 cells or with rIL-1 plus rIL-4; 4) the response of D10 cells to rIL-1 plus rIL-2 also was inhibited by rIFN-gamma, although to a lesser extent. The proliferation of an additional Th2 clone stimulated with rIL-1 plus rIL-4 or rIL-2 also was inhibited by rIFN-gamma, implicating IFN-gamma as an inhibitory lymphokine for Th2 cells in general. rIFN-gamma did not affect the proliferation of two Th1 clones, nor did it affect the proliferation of an unconventional HTL clone which produces both IL-4 and IFN-gamma and proliferates in response to IL-2 or IL-4 in an IL-1-independent fashion. The proliferation of D10 cells stimulated by Ag or by immobilized anti-CD3 antibody also was blocked by rIFN-gamma, whereas IL-4 production in response to these stimuli was unaffected, indicating that proliferation and not general cell function was specifically inhibited. Collectively, these data implicate IFN-gamma as a suppressive factor for the proliferation of the subset of HTL designated Th2, and suggest that the relative amounts of the various lymphokines present during an immune response may direct which T cell types increase in number.
TL;DR: A localized and TCR-independent adhesion provides a stabilizing environment for the subtle ternary inter action, which is dependent upon the fine recognition of all three of its participants.
Abstract: A large body of information about antigen receptors on the surface of T lymphocytes has been gathered in the last five years (1, 2). T cell receptors use a variable region gene pool that is completely distinct from the variable genes of immunoglobulins. Indeed, T cells recognize different antigenic entities than do B lymphocytes. The latter notion was most dramatically demonstrated by the many observations that led to the conclusion that T cell receptors corecognize processed nominal antigen and a gene product of the MHC (3). Since T cell receptors (TCR) and MHC products are anchored in the plasma membrane of T lymphocytes and antigen-pre senting cells, respectively, the TCR/antigen/MHC recognition takes place on the interface between the two cells. A localized and TCR-independent adhesion provides a stabilizing environment for the subtle ternary inter action, which is dependent upon the fine recognition of all three of its participants. From model studies with human cytotoxic T cells, it appears that this transient adhesion event is initiated prior to the interaction of TCR with antigen and MHC (4). The T cell receptors for antigen and MHC consist of two disulfide linked variable glycoproteins whose genes rearrange in T cells: the T cell receptor (TCR) a and /3 chains (1, 2). The T cell receptor so defined subserves both antigen and MHC recognition. Cell fusion experiments (5) and transfection of TCR-a and -/3 chain cDNAs of defined specificities between T cell clones (6) confirm that the a//3 heterodimer confers both
TL;DR: In the periphery of transgenic mice expressing Ld, functional T cells bearing the 2C T-cell receptor were deleted and this elimination of autoreactive T cells appears to take place at or before the CD4+CD8+ stage in thymocyte development.
Abstract: The T-cell repertoire found in the periphery is thought to be shaped by two developmental events in the thymus that involve the antigen receptors of T lymphocytes. First, interactions between T cells and major histocompatibility complex (MHC) molecules select a T-cell repertoire skewed towards recognition of antigens in the context of self-MHC molecules. In addition, T cells that react strongly to self-MHC molecules are eliminated by a process called self-tolerance. We have recently described transgenic mice expressing the alpha beta T-cell receptor from the cytotoxic T lymphocyte 2C (ref. 11). The clone 2C was derived from a BALB.B (H-2b) anti-BALB/c (H-2d) mixed lymphocyte culture and is specific for the Ld class I MHC antigen. In transgenic H-2b mice, a large fraction of T cells in the periphery expressed the 2C T-cell receptor. These T cells were predominantly CD4-CD8+ and were able to specifically lyse target cells bearing Ld. We now report that in the periphery of transgenic mice expressing Ld, functional T cells bearing the 2C T-cell receptor were deleted. This elimination of autoreactive T cells appears to take place at or before the CD4+CD8+ stage in thymocyte development. In addition, we report that in H-2s mice, a non-autoreactive target haplotype, large numbers of CD8+ T cells bearing the 2C T-cell receptor were not found, providing strong evidence for the positive selection of the 2C T-cell receptor specificity by H-2b molecules.
Journal Article•
TL;DR: Intravenous injection of the antibody in the course of T-cell-mediated transfer EAE augmented the severity and duration of clinical signs and resulted in the formation of large, confluent demyelinated plaques.
Abstract: In this study the authors have developed a model with which can be studied directly the influence of circulating anti-myelin antibody on the clinical and pathologic course of inflammatory T-cell-mediated experimental allergic encephalomyelitis (EAE) in the rat. EAE was induced by passive transfer of either myelin basic protein (MBP)-activated spleen cells derived from sensitized donors or long-term-cultured MBP-specific T-cell lines. At the onset of the disease, monoclonal antibodies against a myelin/oligodendrocyte glycoprotein (MOG) were injected intravenously. This antigen is exposed on the surface of central nervous system myelin and oligodendrocytes. Intravenous injection of the antibody in the course of T-cell-mediated transfer EAE augmented the severity and duration of clinical signs and resulted in the formation of large, confluent demyelinated plaques.
Journal Article•
TL;DR: IFN-gamma has an important and perhaps unique physiologic role in the stimulation of IgG2a secretion and in the suppression of secretion of Igg1, whereas bacterial antigens can suppress IgE secretion by other mechanisms in addition to IFN-Gamma secretion.
Abstract: The lymphokine IFN-gamma has been shown in vitro to stimulate IgG2a secretion and inhibit IgG1 and IgE secretion by LPS-activated B lymphocytes. To determine whether IFN-gamma has a similar isotype regulatory role in vivo, we studied the abilities of rIFN-gamma and a mAb to IFN-gamma to modify the isotypes of Ig secreted in mice injected with a goat antibody to mouse IgD, which by itself induces large increases in levels of serum IgG1 and IgE and a relatively small increase in serum IgG2a. Multiple injections of IFN-gamma substantially inhibited production of IgG1 and IgE, and stimulated production of IgG2a in affinity purified goat antibody specific for mouse IgD-treated mice; anti-IFN-gamma antibody blocked the effects of IFN-gamma and in fact enhanced IgG1 and IgE secretion and inhibited the IgG2a response in these mice. The role of IFN-gamma in the selection of isotypes of Ig produced in response to injection of mice with the bacterium Brucella abortus (BA) was also studied, because killed, fixed BA are known to stimulate IFN secretion and a predominantly IgG2a antibody response. Anti-IFN-gamma antibody strongly suppressed IgG2a secretion and stimulated IgG1, but not IgE, secretion in BA-immunized mice. BA suppressed IgG1 and IgE secretion and enhanced IgG2a secretion in affinity purified goat antibody specific for mouse IgD-injected mice; treatment of these mice with anti-IFN-gamma antibody reversed the effects of BA on IgG1 and IgG2a secretion, but not the suppressive effect of BA on IgE secretion. These observations demonstrate that IFN-gamma has an important and perhaps unique physiologic role in the stimulation of IgG2a secretion and in the suppression of secretion of IgG1, whereas bacterial antigens can suppress IgE secretion by other mechanisms in addition to IFN-gamma secretion.
TL;DR: It is demonstrated that a T cell line established against fraction 9, designated line 9, transfers protection equivalent to that obtained by active immunization, and suggested that susceptibility and resistance in experimental leishmaniasis may depend upon a balance between the Th subsets induced.
Abstract: BALB/c mice can be protected against a normally fatal Leishmania major infection by immunization with a partially purified, soluble subfraction of the parasite (fraction 9). In this study, we demonstrate that a T cell line established against fraction 9, designated line 9, transfers protection equivalent to that obtained by active immunization. In contrast, T cell lines (lines 1 and 9.2) responsive to a nonprotective soluble fraction (fraction 1) not only failed to protect BALB/c mice against L. major, but exacerbated the infection. Most importantly, in addition to differing in their antigen specificity, protective and exacerbative T cells lines could be distinguished on the basis of the lymphokines produced, a characteristic previously used to separate murine Th cells into two subsets, designated Th1 and Th2. We found that the protective cell line, line 9, displayed the Th1 property of secreting IL-2 and IFN-gamma, while the exacerbating lines secreted IL-4 and IL-5, a characteristic of Th2 cells. Our results demonstrate that Th1 and Th2 cells may have dramatically different effects on the outcome of an infection, and suggest that susceptibility and resistance in experimental leishmaniasis may depend upon a balance between the Th subsets induced.
TL;DR: The presence of additional immune-related antigens in AD, and distributional differences from normal elderly controls, suggest that the glial proliferation and scavenger activity characteristic of Alzheimer's disease may occur in an immune context and may play an important role in the pathogenesis of the disorder.
TL;DR: Macrophages play a central and essential part in the immune response by presenting antigen to lymphocytes during the development of specific immunity and by serving as supportive, "accessory" cells...
Abstract: MACROPHAGES play a central and essential part in the immune response by presenting antigen to lymphocytes during the development of specific immunity and by serving as supportive, "accessory" cells...
TL;DR: It is concluded that EBV may infect T cells and contribute to lymphomas in selected patients with severe EBV infections.
Abstract: Fatal T-cell lymphomas developed in three patients with a chronic illness manifested by fever, pneumonia, dysgammaglobulinemia, hematologic abnormalities, and extraordinarily high titers of antibody to the Epstein-Barr virus (EBV) capsid antigen (greater than 10,000) and early antigen (greater than 640) but low titers to the EBV nuclear antigen (less than or equal to 40). To understand the pathogenesis of these tumors better, we determined the immunophenotype of the tumor cells and analyzed tumor-cell DNA for EBV genomes and for lymphoid-cell gene rearrangements. More than 80 percent of the cells in tumors had an activated helper T-cell phenotype (T4, T11, la positive). The EBV genome was found by in situ hybridization in tumor tissue from each patient. Southern blot assay of DNA digests from one patient showed the same pattern as that of the EBV-infected marmoset line, B95-8. DNA digests from two patients showed a monoclonal proliferation of T cells determined on the basis of uniform T-cell-receptor gene rearrangements and a single band for the joined termini of the EBV genome. We conclude that EBV may infect T cells and contribute to lymphomas in selected patients with severe EBV infections.
TL;DR: An analysis of the known cytotoxic and helper T cell epitopes has revealed similarity within their primary sequences, arguing that the binding of peptide antigens to class I and class II is similar in nature.
Abstract: An analysis of the known cytotoxic and helper T cell epitopes has revealed similarity within their primary sequences These similar motifs, characteristic of the known determinants, have been incorporated into predictive templates that have been used successfully to define eight helper and three cytotoxic epitopes in four different proteins When the defined epitopes are segregated by restriction element, allele specific subpatterns emerge centering around the general pattern The presence of similarities argues that the binding of peptide antigens to class I and class II is similar in nature In addition, these motifs can be used to predict accurately areas within proteins capable of being recognized by individual MHC class I and class II molecules
TL;DR: The results indicate that the specific interaction of the T-cell receptor on immature thymocyte with thymic major histocompatibility complex antigens determines the differentiation of CD4+8+ thymocytes into either CD4-8– or CD4–8+ mature T cells.
Abstract: T-cell receptors and T-cell subsets were analysed in T-cell receptor transgenic mice expressing alpha and beta T-cell receptor genes isolated from a male-specific, H-2Db-restricted CD4-8+ T-cell clone. The results indicate that the specific interaction of the T-cell receptor on immature thymocytes with thymic major histocompatibility complex antigens determines the differentiation of CD4+8+ thymocytes into either CD4+8- or CD4-8+ mature T cells.
Patent•
TL;DR: The 7E11-C5 monoclonal antibody as mentioned in this paper showed specificity for a non-soluble, membrane associated, organ specific antigenic determinant limited in its distribution to normal and neoplastic, human prostate epithelial cells.
Abstract: Monoclonal antibodies to prostatic cells, are produced by a hybridoma formed by fusing mouse lymphocytes and mouse myeloma cells. The monoclonal antibodies show specificity for a non-soluble, membrane associated, organ specific antigenic determinant limited in its distribution to normal and neoplastic, human prostate epithelial cells. The monoclonal antibodies, specifically 7E11-C5 monoclonal antibodies, may be suitable for diagnostic uses.
TL;DR: By systematically altering surface residues in the mouse IgG2b isotype, the binding site for C1q is localized to three side chains, Glu 318, Lys 320 and Lys 322, which are relatively conserved in other antibody isotypes and a peptide mimic of this sequence is able to inhibit complement lysis.
Abstract: In humoral defence, pathogens are cleared by antibodies acting as adaptor molecules: they bind to antigen and trigger clearance mechanisms such as phagocytosis, antibody-dependent cell-mediated cytotoxicity and complement lysis. The first step in the complement cascade is the binding of C1q to the antibody. There are six heads on C1q, connected by collagen-like stems to a central stalk, and the isolated heads bind to the Fc portion of antibody rather weakly, with an affinity of 100 microM (ref. 3). Binding of antibody to multiple epitopes on an antigenic surface, aggregates the antibody and this facilitates the binding of several C1q heads, leading to an enhanced affinity of about 10 nM (ref. 1). Within the Fc portion of the antibody, C1q binds to the CH2 domain. The interaction is sensitive to ionic strength, and appears to be highly conserved throughout evolution as C1q reacts with IgG from different species (for example see ref. 8). By systematically altering surface residues in the mouse IgG2b isotype, we have localized the binding site for C1q to three side chains, Glu 318, Lys 320 and Lys 322. These residues are relatively conserved in other antibody isotypes, and a peptide mimic of this sequence is able to inhibit complement lysis. We propose that this sequence motif forms a common core in the interactions of IgG and C1q.
TL;DR: It is reported that most mature T cells residing in the murine intestinal epithelium express CD3-associated TCRs composed of γ-chains distilphide-linked to a protein resembling the δ-chain.
Abstract: The vast majority of mature T lymphocytes in the peripheral blood and lymphoid organs use the CD3-associated alpha, beta T-cell receptor (TCR) heterodimer for antigen recognition. A second class of TCRs consists of disulphide-linked gamma and delta proteins that are also CD3-associated. A subset of early CD3+ fetal and adult CD4- 8- thymocytes express gamma, delta TCRs before alpha, beta TCRs are detectable. In addition, a minor (1-5%) subpopulation of peripheral T lymphocytes, and some spleen cells from nude mice express gamma, delta TCRs. Notably, dendritic epidermal cells have also been shown to express gamma, delta TCRs. All of these populations lack CD4 and CD8 molecules. We now report that most mature T cells residing in the murine intestinal epithelium express CD3-associated TCRs composed of gamma-chains disulphide-linked to a protein resembling the delta-chain. The striking feature of these intraepithelial lymphocytes (IEL) was that they were exclusively CD4-8+. In addition, approximately half of CD3-bearing IEL lacked detectable Thy-1 on the cell surface, which is unprecedented for murine T cells. In contrast to other CD8+ peripheral T cells, freshly isolated IEL could be induced to display cytolytic activity by engaging the CD3 molecule, indicating that activation had occurred in vivo. Thus, CD8+ IEL are a phenotypically diverse and anatomically restricted population of lymphocytes that use gamma-chain containing heterodimers for antigen recognition.
TL;DR: There is direct evidence that positive selection of antigen-specific, class I MHC-restricted CD4−8+ T cells in the thymus requires the specific interaction of the αβ TCR with the restricting classI MHC molecule.
Abstract: Thymus-derived lymphocytes (T cells) recognize antigen in the context of class I or class II molecules encoded by the major histocompatibility complex (MHC) by virtue of the heterodimeric alpha beta T-cell receptor (TCR). CD4 and CD8 molecules expressed on the surface of T cells bind to nonpolymorphic portions of class II and class I MHC molecules and assist the TCR in binding and possibly in signalling. The analysis of T-cell development in TCR transgenic mice has shown that the CD4/CD8 phenotype of T cells is determined by the interaction of the alpha beta TCR expressed on immature CD4+8+ thymocytes with polymorphic domains of thymic MHC molecules in the absence of nominal antigen. Here we provide direct evidence that positive selection of antigen-specific, class I MHC-restricted CD4-8+ T cells in the thymus requires the specific interaction of the alpha beta TCR with the restricting class I MHC molecule.
TL;DR: The data suggest that stem cells responsible for hematopoietic reconstitution are CD34+, and these cells are enriched from marrows of five baboons using avidin-biotin immunoadsorption.
Abstract: The CD34 antigen is present on 1-4% of human marrow cells including virtually all hematopoietic progenitors detected by in vitro assays. Since the anti-CD34 monoclonal antibody 12-8 reacts with a similar marrow population in baboons, it was possible to test whether this antigen is expressed by stem cells responsible for hematopoietic reconstitution in vivo. CD34+ cells were enriched from marrows of five baboons using avidin-biotin immunoadsorption. After lethal irradiation, the five animals were given 15-27 X 10(6) autologous marrow cells (3.2-4.4 X 10(6) cells/kg) containing 65-91% CD34+ cells. All animals achieved granulocyte counts greater than 1,000/mm3 and platelet counts greater than 20 X 10(3)/mm3 by 13-24 d posttransplant and subsequently developed normal peripheral blood counts. Two additional animals received 184 and 285 X 10(6) marrow cells/kg depleted of CD34+ cells. One animal died at day 29 without engraftment, while the other had pancytopenia for greater than 100 d posttransplant. The data suggest that stem cells responsible for hematopoietic reconstitution are CD34+.